Heat exchanger for generating steam for solar power plants

ABSTRACT

A heat exchanger erected vertically for generating steam for solar power plants, including: an outer casing with an inlet and an outlet port for a heat-emitting medium; an inlet and an outlet collector for a heat-absorbing medium, said inlet and outlet collectors lying substantially within the outer casing; and a tube bundle within the outer casing with a number of tube layers including continuous tubes, wherein the heat-emitting medium can flow entirely around same and which are designed as flow paths for the heat-absorbing medium from the inlet collector to the outlet collector. The tube bundle is arranged in a meandering manner, wherein the heat exchanger is arranged according to a forced-flow principle so that the heat-absorbing medium is successively pre-heated, evaporated, and superheated so that a superheated steam exits the outlet collector. The energy for the pre-heating, evaporation, and superheating is essentially provided by the heat transfer from the heat-emitting medium to the heat-absorbing medium. The tube layers are arranged in such that the tubes of the individual tube layers are aligned to lie next to one another in the horizontal direction, with the directions of flow of the heat-absorbing medium being opposite in the horizontally adjacent tube sections which are arranged transversely to the central axis of the outer casing, and such that the tube layers are vertically adjacent. Each tube layer is formed from an equal number of tubes.

The invention relates to a heat exchanger for generating steam for solar power plants.

Heat exchangers which are arranged in a modular manner and which operate according to the so-called circulation principle (natural or forced circulation) are known from the state of the art. The heat exchanger comprises a number of heat exchanger modules such as a preheater module, one or several evaporator modules and a superheater module, which are switched together into a functional unit by means of respective inlet and outlet headers, circulation pipes and an external steam collecting drum.

Considerable changes in the load and temperature frequently occur in solar power plants depending on the time of the year, the time of the day and also the weather situation, so that the design of the steam generator for solar-thermal power plants proves to be difficult. Rapid start-up speeds with high temperature gradients, a low need for space and low production and operating costs are only some of the important demands made on a heat exchanger for generating steam for a solar power plant.

Accordingly, there is still a demand for even more compact and more efficient heat exchangers for solar power plants, which in addition can be produced at lower cost and can be operated securely.

That is why the invention is based on the object of providing a heat exchanger which allows a compact configuration, cost-effective production and secure operation.

This object is achieved by a heat exchanger according to the independent claim. Preferred further developments are provided in the dependent claims.

The heat exchanger in accordance with the invention for generating steam for solar power plants comprises an outer casing with an inlet and outlet nozzle for a heat-emitting medium. The exchanger further comprises an inlet and an outlet header for a heat-absorbing medium, preferably water, said inlet and outlet header being arranged substantially within the outer casing. Furthermore, a tube bundle is further disposed within the outer casing, comprising a number of tube layers with continuous tubes which are arranged in such a way that the heat-emitting medium can be flow entirely around the same and which are designed as flow paths for the heat-absorbing medium from the inlet header to the outlet header. The tube bundle is arranged in a meandering fashion. The heat exchanger in accordance with the invention is arranged for generating steam according to the forced-flow principle, so that the heat-absorbing medium which is fed into the inlet header is successively preheated, evaporated and superheated in the course of the flow paths, so that a superheated steam exits from the outlet header. The energy required for the preheating, evaporation and superheating is essentially provided entirely by the heat transfer from the heat-emitting medium to the heat-absorbing medium within the outer casing.

The heat exchanger therefore combines at least three different apparatuses, which are preheater, evaporator and superheater. As a result of the meandering arrangement of the tubes, heat exchange occurs according to the counter-flow or cross-flow principle. A heat-absorbing medium, preferably water, flows through the meandering tubes. As a result of the meandering arrangement of the tube bundles, the overall size of the heat exchanger is reduced in its entirety, the heat transmission from heat-emitting to heat-absorbing medium is improved and further the thermal elasticity of the configuration is increased.

As a result of the configuration of the heat exchanger for generating steam for solar power plants according to the forced-flow principle, i.e. the supplied heat-absorbing medium, preferably water, is preheated “in one passage” from the inlet header to the outlet header, thereafter evaporated and finally superheated, an exceptionally compact and efficient steam generator is realized. Instead of using several separate heat exchanger modules which require an expensive and complex interconnection, the water which enters via the inlet header into the heat exchanger in the fluid state is preheated in the course of its flow within the heat exchanger tubes in the direction towards the outlet header, and is evaporated and superheated, so that superheated steam will leave the heat exchanger via the outlet header, which superheated steam can be supplied to the steam turbine for power generation.

By saving additional steam drums, flow lines and connections between the individual modules, not only are material costs reduced to a substantial extent but also the production and operating costs because a major part of the laborious welding work and the subsequent inspection of the same can be omitted. As a result of avoiding the components which are disposed outside of the outer casing such as a steam drum and various tube lines, a compact configuration is enabled in accordance with the invention and, at the same time, a higher efficiency of the exchanger is achieved because the heat transfer for steam generation substantially only occurs within the outer casing of the heat exchanger and therefore no additional thermal losses will occur as a result of components disposed outside of the outer casing of the heat exchanger.

“Continuous tubes” shall mean in this connection that every tube which respectively defines a flow path for the heat-absorbing medium does not have any branching or mixing points between the inlet header and the outlet header. The tubes further extend completely “within the outer casing”, which means that no parts of the tube bundle are disposed outside of the outer casing and that the heat-emitting medium flows entirely around the tubes. No external energy sources are therefore required which promote preheating, evaporation or superheating. The heating areas of the continuous tubes therefore successively form in the direction of flow the preheater, evaporator and superheater zone. These individual “zones” cannot be recognized from the outside because only one tube bundle is arranged between the inlet header and the outlet header and the tube bundle has a constant progression with a repetitive meandering pattern.

In accordance with a preferred embodiment of the invention, the heat exchanger can be erected either horizontally or vertically. Vertical installation is preferable because it allows an even better utilization of the surface area. Several of the heat exchangers in accordance with the invention can be operated next to one another in parallel on a relatively small surface area. The available space is very limited in solar-thermal power plants because the parabolic trough collectors require a large amount of space. The space-saving configuration of the heat exchanger in accordance with the invention allows a nearly remote installation, so that the flow paths of the heated media to the heat exchanger can appropriately be reduced. The temperatures of the heat-emitting medium are higher when entering the heat exchanger, so that the heat yield will be improved.

A further preferred embodiment of the invention provides that the tube bundle comprises a number of vertical tube layers in the case of vertical installation, with each tube layer being formed by the same number of tubes, and that the tube layers are arranged in such a way that the tubes of the individual tube layers are aligned in the horizontal direction to lie precisely next to one another, with the directions of flows of the heat-absorbing medium being in opposite directions in the horizontally adjacent tube sections which are arranged transversely to the central axis of the outer casing. The arrangement of the tube bundles in individual tube layers allows an extremely compact configuration. Since the tubes can be disposed precisely next to one another horizontally, conventional spacers can be used between the tubes. The opposite flow in the horizontally adjacent tube sections which are arranged transversely to the central axis of the outer casing promotes the symmetric temperature distribution in the heat exchanger with respect to the central axis. The same also applies to the horizontal installation of the heat exchanger. In this case, the tube layers are disposed horizontally above one another, but twisted by 90° in comparison with the vertical installation.

Preferably, the inlet and the outlet headers have a circular cross-section. The tubes of one tube layer on one circumferential line of the inlet and outlet header are connected with the inlet and outlet header offset from one another by the same angle. The production process will be facilitated in this way because sufficient space is provided for welding work, production by metal cutting or other work on the headers.

The tubes of the adjacent tube layers are further preferably connected with the inlet and outlet headers in such a way that the tubes of the one tube layer are arranged with respect to the tubes of the adjacent tube layer offset by an angle on an adjacent circumferential line of the respective inlet and outlet header. As a result, the circumferential areas of the inlet and outlet headers can be utilized optimally, so that the arrangement of the tube layers can be provided with a compact configuration. There is still sufficient space for welding work, production by metal cutting or other work on the headers.

In accordance with a further embodiment of the invention, the tube bundle comprises a separate section in which the preheating of the heat-absorbing medium mainly occurs. The separate preheater section can be realized by a local separation within the outer casing for example. It is also possible to control the flow of the heat-emitting medium and therefore the distribution of the temperature in the heat exchanger in such a way that the preheating of the heat-absorbing medium mainly occurs in this preheater section. Alternatively, the preheating could also occur completely outside of the outer casing, i.e. in a separate preheater. In this case, the heat exchanger in accordance with the invention would be arranged mainly for the evaporation and the superheating of the heat-absorbing medium.

In accordance with a further embodiment of the invention, the tube bundle comprises a separate section in which the evaporation of the heat-absorbing medium mainly occurs. The separate evaporator section can be realized for example by a local separation within the outside jacket. It is also possible to control the flow of the heat-emitting medium and consequently the distribution of the temperature in the heat exchanger in such a way that the evaporation of the heat-absorbing medium mainly occurs in this evaporator section. Alternatively, the evaporation could also occur completely outside of the outer casing, i.e. in a separate evaporator. In this case, the heat exchanger in accordance with the invention would be arranged mainly for the preheating and the superheating of the heat-absorbing medium.

In accordance with a further embodiment of the invention, the tube bundle comprises a separate section in which the superheating of the heat-absorbing medium mainly occurs. The separate superheater section can be realized for example by a local separation within the outside jacket. It is also possible to control the flow of the heat-emitting medium and consequently the distribution of the temperature in the heat exchanger in such a way that the superheating of the heat-absorbing medium mainly occurs in this superheater section. Alternatively, the superheating could also occur completely outside of the outer casing, i.e. in a separate superheater. In this case, the heat exchanger in accordance with the invention would be arranged mainly for the preheating and the evaporation of the heat-absorbing medium.

Preferably, the tubes are connected via nipples with the inlet and outlet header. This simplifies the connection of the compact tube bundle at the inlet and outlet header. The connection between the nipples and the individual tubes preferably occurs by material connection, e.g. by welding. The welding process can occur in an automated manner. Thereafter, the weld seams are checked individually, e.g. by means of x-rays.

In a preferred embodiment of the invention, the tubes are directly connected with the inlet and outlet header without nipples. In this case too, the connection between the headers and the individual tubes preferably occurs by material connection, e.g. by welding. The welding process can also occur in an automated manner. Thereafter, the weld seams are checked individually, e.g. by means of x-rays.

Preferably, the nipples are materially connected with the inlet and outlet header by means of welding for example. The welding process can also be performed automatically in this case too.

In accordance with a further embodiment of the invention, the nipples are made directly by means of metal cutting from the material of the inlet and outlet header. For example, the nipples can be milled out of the initially tubular material of the inlet and outlet header. Potential damage caused by welding work is reduced thereby.

Furthermore, the examination of the individual weld seams between the nipples and the respective header can be avoided thereby.

In accordance with a preferred further development of the invention, the tubes of the tube bundle are arranged in an internal housing which is arranged concentrically within the outer casing and comprises an inlet and outlet opening for the heat-emitting medium. The cross-sectional profile of the internal housing is preferably rectangular, so that the tube bundle is enclosed as tightly as possible by said internal housing. As a result of the additional enclosure of the heat-exchanging components, a further insulation is achieved between the heat exchanger modules and the surrounding environment. The inlet and the outlet opening of the internal housing can be connected with the corresponding inlet and outlet nozzles in such a way that a separate space is created between the outer casing and the internal housing. Alternatively, a flow of the heat-emitting medium can be permitted along the inside wall of the outer casing.

In an advantageous embodiment of the invention, the inlet and the outlet nozzles for the heat-emitting medium are arranged in the bottom part of the outer casing in the case of a vertical installation of the heat exchanger. The compactness of the heat exchanger is increased even further thereby. Furthermore, maintenance work is facilitated thereby because the connections on the casing side are arranged close to the bottom part. The space between the outer casing and the internal housing is used as a flow channel for the heat-emitting medium. The hot heat-emitting medium enters via the inlet nozzle of the outer casing and the inlet opening of the internal housing into the interior of the internal housing and flows upwardly. Thereafter, the heat-emitting medium flows through the annular flow channel which is produced by the concentric arrangement of the outer casing and the internal housing, then back downwardly where it then exits the outer casing via the outlet nozzle. The dwell time of the heat-emitting medium in the heat exchanger is increased thereby, so that the heat transmission to the heat-absorbing medium is generally improved.

The invention will be explained below in closer detail by reference to the drawings, which show schematically:

FIG. 1 shows a side view of an embodiment of the heat exchanger in accordance with the invention;

FIG. 2 shows a sectional view along the line A-A of FIG. 1;

FIG. 3 shows a detailed view “X” of FIG. 2;

FIG. 4 shows a sectional view along the line B-B of FIG. 3;

FIG. 5 shows a detailed view of the inlet header of FIG. 1 and FIG. 2;

FIG. 6 shows a top view of the inlet header of FIG. 5.

FIGS. 1 and 2 show an embodiment of the heat exchanger 1 in accordance with the invention. The heat exchanger 1 is vertically erected in a space-saving manner. An inner housing 3 is disposed within the outer casing 2, which inner housing has a rectangular cross-sectional profile. The meandering tubes of the tube bundle 11 are arranged in the inner housing 3. The heat-absorbing medium such as water enters the heat exchanger 1 via the inlet header 6. After flowing through the tubes of the tube bundle 11, it exits from the heat exchanger 1 via the outlet header 7. The water is preheated and thereafter evaporated and subsequently superheated on the path from the inlet header 6 to the outlet header 7. The superheated steam which exits from the heat exchanger 1 is guided for power generation to the downstream steam turbine (not shown). The individual “zones”, which are preheater, evaporator and superheater, are not visible from the outside. The heat exchanger 1 for the generation of steam, which works according to the forced-flow principle such as the Benson principle, generates a superheated steam in the course of the flow within the heat exchanger 1 from the feed water which enters in fluid form into the inlet header, which superheated steam can be taken from the outlet header 7. As a result, the conventionally used steam drums, circulation pipes, inlet and outlet headers and numerous weld seams can be omitted, so that the compactness is increased and production costs can be saved. The claws 8 are used for mounting the heat exchanger 1. Maintenance work can be performed in a simple manner via manholes 9 which comprise transparent glass windows and/or locking means.

The heat-emitting medium preferably concerns thermal oil which is heated in the absorber tubes of the parabolic fluted reflectors to approximately 400° C. Fluid salts or other suitable heat carrier media could be used as an alternative. The thermal oil enters the heat exchanger 1 via the inlet nozzle 4 of the outer casing 2. It flows from there in the direction of the outlet nozzle 5 and flows about the tube bundle 11 which is shaped in a meandering manner. Once the thermal oil has transferred a portion of its thermal energy to the water, it exits from the heat exchanger 1 via the outlet nozzle 5.

In accordance with an embodiment (not shown), the flow of the thermal oil on the casing side can be guided in such a way that the thermal oil will enter and exit in the bottom part of the heat exchanger 1. The space between the inner housing 3 and the outer casing 2 is used as a flow path for the downwardly flowing thermal oil. In this case, both the inlet nozzle and also the outlet nozzle are arranged in the bottom region of the vertically erected heat exchanger 1.

Two tubes of a tube layer are indicated in FIG. 2. It is understood that the number of the tubes and the tube layers of a tube bundle 11 are adjusted according to the different conditions. FIG. 3 shows a tube layer 20 with the four tubes 21, 22, 23, 24 for example. It clearly shows the meandering structure of the tube bundle 11.

FIG. 4 illustrates the arrangement of the individual tube layers 20, 30 with respect to each other. In the tube sections 15 (FIG. 3) which are arranged transversely to the central axis 10 of the outer casing 1, each tube has an opposite direction of the tube flow with respect to its horizontally adjacent tube in the case of vertical installation. This means for example that the flow in the tube 21 is opposite to the flow in the horizontally adjacent tube 34. This opposite flow in the respectively adjacent tube layers 20, 30 additionally ensures a constant temperature distribution within the heat exchanger 1. As a result of the constant and compact arrangement of tubes and tube layers with respect to each other, simple spacers 12 can be used.

FIG. 5 shows a header in accordance with the invention on an enlarged scale. It concerns the inlet header 6. The inlet and outlet headers 6, 7 differ only slightly from one another. The nipples 22 a, 33 a are clearly recognizable, which are used for fastening the tubes 22, 33 to the inlet header 6. The nipples 21 a, 22 a, 23 a, 24 a and therefore also the tubes 21, 22, 23, 24 of the first tube layer 20 are disposed on a first circumferential line 13 and respectively open into the header 6 offset by the same angle a. Similarly, the tubes 31, 32, 33, 34 with the same nipples 31 a, 32 a, 33 a, 34 a enter the header 6 on an adjacent circumference line 14 offset by the same angle α.

FIG. 6 shows a top view of the header 6. The angle α, by which a tube of one layer is offset from the next tube of the next layer, is in this case 45° each. The second layer 30 which is adjacent to the first layer 20 is arranged to be offset by precisely β=22.5° in relation to the first layer 20, so that the tubes 31, 32, 33, 34 of the second layer 30 in FIG. 6 are respectively visible in the middle between the tubes 21, 22, 23, 24 of the first layer 20. As a result of this regular horizontally and vertically offset arrangement of nipples on the header 6, there will still be sufficient distance for welding work or other production steps despite the high level of compactness. 

1. A heat exchanger for generating steam for solar power plants, with the heat exchanger being erected vertically, comprising: an outer casing with an inlet nozzle and an outlet nozzle for a heat-emitting medium; an inlet header and an outlet header for a heat-absorbing medium, preferably water, with the inlet header and the outlet header being arranged substantially within the outer casing; and a tube bundle within the outer casing with a number of tube layers with continuous tubes which are arranged so that the heat-emitting medium can flow around said tubes completely and which are arranged as flow paths for the heat-absorbing medium from the inlet header to the outlet header; wherein the tube bundle is arranged in a meandering manner, with the heat exchanger for generating steam being arranged according to a forced-flow principle, so that the heat-absorbing medium supplied to the inlet header is successively subjected in the course of the flow paths to a preheating, an evaporation and a superheating, so that superheated steam exits from the outlet header; the energy required for the preheating, evaporation and superheating is made available substantially solely by heat transfer from the heat-emitting medium to the heat-absorbing medium within the heat exchange; the tube layers are arranged in such a way that the tubes of the individual tube layers are aligned to lie precisely next to one another in the horizontal direction, with the directions of flow of the heat-absorbing medium being opposite in the horizontally adjacent tube sections which are arranged transversely to the central axis of the outer casing, and such that the tube layers are vertically adjacent; and each tube layer is formed from an equal number of tubes. 2.-3. (canceled)
 4. The heat exchanger according to claim 1, wherein the inlet header and the outlet header have a circular cross section, and the tubes of a tube layer are connected with the inlet header and outlet header on a circumferential line of the inlet header and outlet header offset from one another by the same angle.
 5. The heat exchanger according to claim 1, wherein the tubes of the adjacent tube layers are connected with the inlet header and outlet header in such a way that the tubes of the one tube layer are arranged with respect to the tubes of the adjacent tube layer offset by an angle on an adjacent circumferential line of the inlet header and outlet header.
 6. The heat exchanger according to claim 1, wherein the tube bundle comprises a separate section in which mainly the preheating of the heat-absorbing medium occurs.
 7. The heat exchanger according to claim 1, wherein the tube bundle has a separate section in which mainly the evaporation of the heat-absorbing medium occurs.
 8. The heat exchanger according to claim 1, wherein the tube bundle has a separate section in which mainly the superheating of the heat-absorbing medium occurs.
 9. The heat exchanger according to claim 1, wherein the tubes are connected with the inlet header and outlet header via nipples.
 10. The heat exchanger according to claim 1, wherein the tubes are directly connected without nipples with the inlet header and outlet header.
 11. The heat exchanger according to claim 9, wherein the nipples are materially connected with the inlet header and outlet header.
 12. The heat exchanger according to claim 9, wherein the nipples are made by metal cutting from the material of the inlet header and outlet header.
 13. The heat exchanger according to claim 1, characterized in that wherein the tube bundle is arranged in an inner housing which is arranged concentrically within the outer casing and comprises an inlet and an outlet opening for the heat-emitting medium.
 14. The heat exchanger according to claim 1, wherein the inlet and the outlet nozzle for the heat-emitting medium is arranged in the bottom part of the outer casing for a vertical installation of the heat exchanger. 